238 Hailey and Percival: Comparative Assessment of Phosphite Formulations for Apple Scab tive phosphite formulations may potentially have a higher efficacy against fungal pathogens, such as apple scab. Comparison of their efficacy has, however, received little attention (Lobato et al. 2008). Certain metal cations, such as copper and zinc, are well recognized for their anti-microbial effects when applied at low concentrations (Nägeli 1893). Indeed, foliar sprays of copper are one of the oldest forms of pathogen control, acting in a protective fashion (Johnson 1935). Cations such as calcium and silicon are linked to improved disease resistance by indirect manipulation of host plant physiology. Applications of calcium, for example, increase cell wall strength through esterification of cellular membranes, thereby enhancing resistance to fungal and bacterial enzymatic degradation (Marschner 2012). Sili- con is a major mineral constituent of plants that enhances growth and can strengthen cell wall integrity as well as mitigate abiotic stresses, such as nutrient imbalance, salinity, drought, and UV damage (Epstein 1999; Epstein 2001; Liang et al. 2005; Currie and Perry 2007; Marschner 2012). Silicon also has SIR activity (Fauteux et al. 2006). Aims of this study were to evaluate five phosphite formulations for plant protec- tion purposes against the biotrophic foliar pathogen apple scab under field conditions. MATERIALS AND METHODS Trial Site The apple trial site consisted of a 0.75 ha block of apple (Malus cv. Golden Delicious) interspersed with individual trees of Malus cv. Red Delicious and cv. Gala as pollinators. Golden Delicious was chosen for the experiment due to its susceptibil- ity to apple scab infection. Planting distances were based on 2 m × 2 m spacing. The trees were planted in 2003 and trained under the central-leader sys- tem to an average height of 2.5 m ± 0.25 m with mean trunk diameters of 12 cm ± 1.4 cm at 45 cm above the soil level. The trial sites were located at the University of Reading Shinfield Experimental Site, University of Reading, Berkshire (N51°43, W-1°08). The soil was a sandy loam containing 4%–6% organic matter, pH of 6.2, and available P, K, Mg, Na, and Ca of 52.0, 659.1, 175.2, 49.4, and 2188 mg l-1 , respectively. Weeds were controlled ©2014 International Society of Arboriculture chemically using glyphosate (Roundup; Green- Tech, Sweethills Park, Nun Monkton, York, UK) throughout experiments. No watering or fertiliza- tion was applied during the trial. Historically, the apples suffered from apple scab infection on an annual basis (Percival et al. 2009). The experiment was conducted in 2012. The treatments, five phos- phite formulations, one fungicide, were applied in eight randomized complete blocks plus a water control with a single tree as the experimental unit. Fungicide and Phosphite Treatments Trees were sprayed until runoff four times through- out the growing season in accordance with specific phenological stages; bud break (March 23), green cluster (April 5), 90% petal drop (May 23), and early fruitlet formation (June 9) (Bevan and Knight 2001), with a range of phosphites and a water con- trol (Table 1). For all phosphite formulations, a dilution of 10 ml per liter of water was used. In addition, a comparative evaluation of a conven- tional synthetic fungicide penconazole (trade name Topas), used within the UK for apple scab control, applied at 1.5 ml per liter of water was undertaken. All phosphite products and penco- nazole fungicide were supplied by Orion Future Technology Ltd. (Henwood House, Henwood, Ashford, Kent). Eight trees per treatment were used. Table 1. Phosphite formulations and synthetic fungicide applied to apple (Malus cv. Golden Delicious) against apple scab, Venturia inaequalis. Product Penconazole Potassium phosphite Zinc phosphite Silicon phosphite Copper phosphite Calcium phosphite Formula C13 H15 H2 O6 Si3 KO3 P2 Cu3 Ca3 Zn3 (PO3 PO3 O6 )2 P2 Scab Severity and Yield Assessment Scab severity of leaves and fruit was assessed visually. Leaf scab severity of each tree was rated using a visual indexing technique and ratings on a 0–5 scale: 0 = no scab observed; 1 = less than 5% of leaves affected and no aesthetic impact; 2 = 5%–20% of leaves affected with some yellow- ing but little or no defoliation; 3 = 21%–50% of leaves affected, significant defoliation and/or leaf yellowing; 4 = 51%–80% of leaves affected, severe Cl2 P N3
July 2014
| Title Name |
Pages |
Delete |
Url |
| Empty |
Search Text Block
Page #page_num
#doc_title
Hi $receivername|$receiveremail,
$sendername|$senderemail wrote these comments for you:
$message
$sendername|$senderemail would like for you to view the following digital edition.
Please click on the page below to be directed to the digital edition:
$thumbnail$pagenum
$link$pagenum
Your form submission was a success. You will be contacted by Washington Gas with follow-up information regarding your request.
This process might take longer please wait
